backend/drm: Ensure plane rotation is always reset
The rotation property of a plane persists between commits. If any application has set the property before wlroots takes over, then that rotation will still apply to wlroots' output. If the rotate applied to a primary plane but not the cursor plane (as would happen if the kernel command line contains "video=HDMI-A-1:1920x1080,rotate=180"), then system operation becomes "interesting".
Always set the rotation to DRM_MODE_ROTATE_0 to ensure that the system generates the expected output.
Signed-off-by: Dave Stevenson dave.stevenson@raspberrypi.com